1. Field of the Invention
The present invention relates generally to the removal of accumulated contaminant deposits on the heat transfer media of regenerative thermal oxidizers. More particularly, the present invention provides an apparatus and method for conducting a burnout of regenerator heat transfer media beds, while eliminating any discharge of visible unburned contaminants, which may be accomplished in an off-line condition for the oxidizer or a flow through on-line condition of the oxidizer. The present system is provided in combination with a purge system employed in normal operation of the oxidizer to preclude venting of unburned contaminants to the atmosphere during changeover between regenerators in a multiple regenerator system.
2. Description of the Prior Art
Regenerative incinerator systems use gas flow reversal to recapture heat, which would otherwise be lost to the atmosphere, during thermal oxidation of volatile contaminant compounds. A regenerative incinerator system consists of a gas heating regenerator which receives the processed gas from the system producing the volatile contaminants, a burner and retention chamber to oxidize the processed gas, and a regenerator which is heated by the exiting gas to cool the gas and reclaim the heat of the combustion process. After a period of time, flow of the gas through the system is reversed whereby the regenerator previously employed in heat recovery, now becomes the heating regenerator and the gas heating regenerator becomes the cooling regenerator through which gas passes prior to being released to the atmosphere thereby again raising the temperature of that regenerator bed.
Regenerator systems employing flow reversal in early systems allowed unburned gases in the inlet regenerator to be released to the atmosphere during the flow reversal. Use of multiple regenerator canisters with purge systems for removal of the unburned gas during flow reversals, eliminates this source of pollution. Certain prior art regenerative incinerator systems use positive pressure within the bottom of the idle regenerator to purge the unburned gases prior to flow reversal. Fresh air or incinerated air is introduced into the bottom of the idle regenerator which forces the residual gas through the media bed and into the combustion chamber. Use of positive pressure purging in this manner requires additional fan capability in the exhaust fan for the system and requires burning of recycled incinerated air thereby increasing fuel usage.
An improved system employing an induced draft purge is disclosed in U.S. Pat. No. 5,026,277 entitled REGENERATIVE THERMAL INCINERATOR APPARATUS, issued to James A. York on Jun. 25, 1991 which is assigned to the assignee of the present invention. The device disclosed in York uses negative pressure rather than positive pressure to purge the idle regenerator. The residual gas within the idle regenerator is removed by suction from the combustion air fan prior to flow reversal.
Operation of regenerative systems such as that disclosed in York and in U.S. Pat. Nos. 3,634,026 to Kuechler, issued Jan. 11, 1972, and U.S. Pat. No. 3,870,474 to Houston, require shutdown of the system to clean the regenerative beds of contaminant deposits which become entrapped in the heat transfer media. Removal of these contaminant deposits requires baking or burnout of the heat transfer media at temperatures sufficient to volitize the contaminant deposits on the heat transfer media. Previously, the volatilized contaminants were emitted to the atmosphere, thus causing a pollution problem. Typical prior art systems require removal of the heat transfer media from the beds in the regenerator canisters for burnout of the contaminant deposits. Alternative techniques such as that disclosed in Houston for removal of portions of the contaminated heat transfer media at the bottom of the regenerator with replacement of fresh heat transfer media at the top of the regenerator reduces the down time of the regenerator, and in some possible cases, could allow operation of the incinerator during media change out. The use of multiple canisters wherein one or more regenerators is idle during a process cycle, allows such operation.
The difficulty of performing such maintenance during operation of the system, including the potential hazards of an operating high temperature system, renders these methods less than ideal.
It is, therefore, desirable to provide a system for burnout of the regenerator media beds without removal of the media and while allowing minimal system down time, or continued operation of the system in incineration of the processed gas during burnout of one or more of the regenerators.
The present invention provides the capability to conduct a burnout of the trapped contaminant compounds in the media of the regenerators without removal of the media. The combination of the burnout feature of the present invention with an induced draft purging system avoids redundancy in system elements and provides maximum efficiency. The primary feature of this invention is that burnout of the regenerators is accomplished without the discharge of visible unburned contaminants to the atmosphere and may be accomplished while incineration of process gas is continued.